I am currently working on my doctoral thesis at the German Aerospace Center (DLR). Here I am working on the development of the terrestrial navigation system R-Mode. The main goal of my PhD thesis is to develop an R-Mode receiver and to test different algorithms in hardware-in-the-loop simulations. I am also using Keysight instruments, among others, to measure the amplifiers used in the R-Mode transmitter.

However, because of Covid19, I lost access to the lab. As an engineer working only on theory is not an option for me, so I decided to develop a low cost R-mode receiver at my own expense. As a PhD student my resources are of course very limited. So far I have a simple toolkit, a NanoVNA and a homebuilt DC power source. My first picture shows my current workbench.

My overall low-cost design uses an RTL SDR in direct sampling mode, a home-built bandpass filter, and a home-built LNA. All signal processing will be done on a single-board computer like the Raspberry Pi.

So far I have designed the bandpass filter, which I could only verify with my nanoVNA (Figure 1).  Because of the non-existing calibration this measurement device cannot be used in my thesis. Also, initial field tests have shown that the insertion loss of the filter is too large to be used without LNA (Figure 2). Accordingly, my next step is to build the amplifier, starting with the preparation of a suitable power source, since I have none at hand.

Development of my low-cost receiver would allow me to complete my PhD thesis on the topic I have in mind in a timely manner. All components are needed in my project. With the signal generator I would be able to do hardware-in-the-loop testing as originally planned. The oscilloscope would be used to calculate the step response of my components. The DC power supply would provide the needed DC voltage for my LNA design and finally the DMM would be useful for general debugging, especially if I go further to FPGA implementation.


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